By the use of the pump and probe THz generation technique, PC antennas made by low temperature growth GaAs (LT-GaAs) were widely investigated [
3–
6], and the results demonstrate that two filed screening effects determine the device response: The screening of the applied bias field due to the space charge induced by the separation of the electrons and holes is as well as the screening of the local filed by the THz radiation. The time behavior of the radiation and space-charge fields was investigated and the results demonstrate that in the initial time the radiation field is very stronger than the space-charge field so that radiation field screening dominates the early response for a LT-GaAs PC H-shaped antenna with a 5-μm-wide PC gap [
6]. For the PC antenna made by GaAs, the investigation on the time behavior of the two fields was missing [
7–
9]. Because the screening effect is the principal cause for saturation of THz emission observed when the emitters are driven hard with high-repetition-rate femtosecond (fs) laser pulses, this miss leads to that people do not fully understand the working process and characteristic of THz emitter made by GaAs.